EXCITONIC N-STRING IN LINEAR-CHAINS - ELECTRONIC-STRUCTURE AND OPTICAL-PROPERTIES

The electronic structure and the optical properties of an excitonic n- string which is a bound state of n Frenkel excitons (n = 2,3,...) are theoretically clarified. The binding mechanism may be attributed to th e electrostatic dipolar interaction among the Frenkel excitons, which is in contrast to the formation mechanism of the otherwise analogous e xcitonic molecules in a system of Wannier excitons; it makes it possib le to form bound states of more than two Frenkel excitons, The effects of the n-string states on the electronic structure and optical proper ties are studied. The two-photon absorption and the differential trans mission spectra are shown to depend strongly on the direction of the i nduced static dipole moment, which determines whether the interaction between excitons is attractive or repulsive.